In the United States, many houses are wired with a 110-volt electrical system. Electrical outlets (located in walls, etc.) are adapted to provide 110 volts to power lights and other appliances.
Recently, 12-volt devices have been developed which may be powered, for example, using a cigarette lighter in an automobile. Specially designed 12-volt plugs have been developed to fit into an automobile cigarette lighter and provide power to such devices.